Operating Frequency Limit Research Articles

Photonic-assisted RF phase difference detector with full 0° to 360° phase detection capability

A microwave photonic structure for detecting the phase difference of two radio frequency (RF) signals is presented. It is capable of determining the RF signal phase difference unambiguously over the full 0° to 360° range, which overcomes the 0° to 180° phase detection range limitation in the reported structures. The proposed RF phase detector is designed to generate two DC voltages with amplitudes depending on the phase difference of the two input RF signals. An RF signal phase difference in the 0° to 360° range can be obtained from the ratio of the two system output DC voltages. The proposed RF phase detector has a wide operating frequency range, as it is free of microwave components. It overcomes the drawbacks of complex structures, large phase detection errors, limited phase detection range, and limited operating frequency range in the reported photonics-based RF phase detectors. Experimental results are presented that demonstrate 0° to 360° phase difference detection with errors below ±3∘ for different input RF signal frequencies.

POWER SUPPLY OF RING ANTENNA USING DIRECTIONAL COUPLERS

Context. The circular polarization of radio waves is used in various electronic systems. This includes, for example, space communications stations, some radio relay communication systems, radar stations, data transmission systems and others. The characteristics of radio wave propagation are studied by using electromagnetic waves separated by circular orthogonal polarization in radiomonitoring and radiocontrol systems. Compared to other antenna types, circularly polarized antennas, such as rings, have superior design simplicity and excellent electrodynamics properties.
 Objective. The objective of this study is to analyse the characteristics and application of directional microstrip couplers for supplying power to ring antennas.
 Method. To better the performance of microstrip ring antennas, the reasons for their limited operating frequency range are analysed. These causes include the frequency-dependent parameters of the coupler, errors in calculating the directional coupler circuit, and radiation from asymmetric strip lines. To understand how supply lines, affect antenna characteristics, correlations between radiation fields determined in both its coordinate system and that of the primary axis are taken into account.
 Results. An analysis of the dependence graphs of the main characteristics of ring microstrip antennas with intricate power supply circuits for directional couplers and comparison with similar characteristics for simple circuits revealed that the shape of the radiation pattern in the higher radiation hemisphere became symmetrical about the axis, especially when symmetrically supplying the ring with branch-line couplers. The frequency band has also widened, at which there was an acceptable degree of deviation in the ellipticity coefficient from unity.
 Conclusions. The simulation results of microstrip ring antennas with power lines connected to directional couplers of different types showed that supplying the ring antenna with electricity via the directional coupler ensures circular polarization for the emitted electromagnetic waves. Additionally, the range of operating frequencies where there is only a small discrepancy in ellipticity coefficient remains at an acceptable level of –3 dB is quite broad. By utilizing directional branch-line couplers to power a ring antenna, it is possible to simultaneously emit both right and left circularly polarized waves with the same antenna.

Design and Analysis of LLC Resonant Converter With Valley Switching Control for Light-Load Conditions

The LLC converter has been widely used in the power supply industry for its high conversion efficiency. When the output load is low, the LLC resonant converter will substantially increase the operating frequency, thereby reducing the conversion efficiency and exceeding the limited operating frequency of the specification. Thus, burst-mode control is applied to increase the ability of regulation at light-load conditions. Even so, the switching period of power switches still occurs at a high switching frequency. Burst-mode control will also result in an extremely low-frequency output voltage ripple. In this study, a valley switching control (VSC) for the LLC resonant converter at light-load conditions is proposed. The VSC control strategy maintains the output voltage by modulating the pulsewidth signals of drivers and achieves valley switching by modulating the switching frequency. Thus, the VSC strategy can reduce the operating frequency compared with the frequency modulation strategy. Compared with burst-mode operations, the proposed VSC effectively reduces the switching loss and has the advantage of high-frequency output voltage ripple. The VSC increases the efficiency and the power quality of the converter. Detailed analysis and design of the proposed method are described. Experimental results are recorded for a prototype converter with a dc input voltage of 400 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm {DC}}$ </tex-math></inline-formula> , an output voltage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$48~V_{\mathrm {DC}}$ </tex-math></inline-formula> , and an output current of 12.5 A.

A time latch for high speed time‐based ADCs

This letter presents a novel time latch for high speed time domain analogue to digital converters. The time latches reported in literature suffer from a limited maximum operating frequency, which makes them unsuitable for high frequency applications. Analysis of the proposed time latch shows it can operate at 10 GHz, 2.5x higher than the best reported time latch. Furthermore, simulations in 28 nm CMOS technology confirm that the enhancement in the speed of the proposed time latch comes with low overhead in area and power. Potential design issues with the proposed time latch are also discussed.

Composite Amplitude-Shift Keying for Effective LED-Camera VLC

LED-Camera Visible Light Communication (VLC) is gaining increasing attention, thanks to its readiness to be implemented with Commercial Off-The-Shelf devices and its potential to deliver pervasive data services indoors. Nevertheless, existing LED-Camera VLC systems employ mainly low-order modulations such as On-Off Keying (OOK) given the simplicity of their implementation, yet such rudimentary modulations cannot yield a high throughput. In this paper, we investigate various opportunities of using a high-order modulation to boost the throughput of LED-Camera VLC systems, and we decide that Amplitude-Shift Keying (ASK) is the most suitable scheme given the limited operating frequency of such systems. However, directly driving an LED to emit different levels of luminance may suffer heavy distortions caused by the nonlinear behavior of LED. As a result, we innovatively propose to generate ASK using the composition of light emission. In other words, we digitally control the On-Off states of several groups of LED chips, so that their light emissions compose in the air to produce various ASK symbols. We build a prototype of this novel ASK-based VLC system and demonstrate its superior performance over existing systems: it achieves a rate of 2 kbps at a 1 m distance with only a single LED luminaire for static users and more than 1 kbps for mobile users.

Frequency and Phase-Shift Control of Inductive Power Transfer for EV Charger with LCCL-S Resonant Network Considering Misalignment

In inductive power transfer (IPT) systems for electric vehicle applications, the coupling coefficient k and self-inductances of the pads can vary depending on the misalignment and vertical distance due to the presence of loosely coupled pads. Furthermore, the operating frequencies of IPT systems are restricted by a Society of Automotive Engineers standard. These frequencies lead to increases in volt-ampere rating and switching losses. Therefore, this paper proposes a control method for operation in a zero voltage switching region close to the zero phase angle frequency for a low volt-ampere rating considering k and the self-inductance variation in a limited operating frequency range. A mathematical analysis is performed, and the critical coupling coefficients of the proposed control are derived. Simulation and experimental results using a 3.3 kW IPT prototype are presented so as to verify the numerical analysis.

Burst-Mode and Phase-Shift Hybrid Control Method of LLC Converters for Wide Output Range Applications

For an LLC converter, it is difficult to realize the wide output range with conventional pulse frequency modulation control because of the limited operating frequency. This paper proposes a new hybrid control method. The proposed strategy combines the burst-mode control and phase-shift control methods for the LLC converter. The burst-mode control can regulate the output voltage from zero to its maximum value, and the phase-shift control can reduce the increased resonant current during burst-on time. By using this method, the wide output voltage range is realized with the low resonant current during burst-on time and zero-voltage switch (ZVS) for all switches. The reliability and efficiency of the converter can be improved accordingly. The burst duty ratio is regulated by the reference output voltage, and the phase-shift angle is derived when realizing ZVS for lagging-leg switches. Moreover, the resonant parameters and the maximum phase-shift angle are optimized under the constraints of current stress and ZVS condition. This method is easy to be implemented in a low-cost microcontroller because high-frequency real-time calculations are not necessary. A 1.5-kW prototype is built to verify the feasibility and validity of the proposed control method.

Range Coherence Factor for Down Range Sidelobes Suppression in Radar Imaging Through Multilayered Dielectric Media

In radar imaging applications through layered dielectric media, an antenna array with a limited operating frequency bandwidth at the low end of the microwave band is usually employed to probe the target space of interests. As a result, the focused radar imagery is characterized by severe sidelobes in the down-range direction, which leads to the degradation of the image quality. Several techniques, such as windowing and apodization filtering combined with phase coherence factor (PCF) filtering, have been reported to suppress the down-range sidelobes. However, these approaches either expand the main lobe width or are sensitive to parameter tuning. In this paper, by investigating the distribution characteristics of the down-range sidelobes among sub-frequency radar imageries, a robust and efficient range coherence factor (rCF) technique is proposed to suppress the down-range sidelobes in the focused radar imagery. The performance of the proposed approach is assessed by the finite-difference time-domain (FDTD)-based numerical simulations as well as onsite experiments to verify its sidelobes' reduction capabilities.

W-Band High-Q Microwave Photonic Filter With the Third-Order Dispersion Precompensation

A scheme to perform high-quality (high-Q) W-band (75-110 GHz) microwave photonic filters (MPFs) with tunability and reconfigurability is proposed and experimentally demonstrated. The analysis reveals an inverse proportional relationship between the operating frequency of the MPF and the compensatory ability of the optical spectrum processor (OSP) when mitigating the third-order dispersion (TOD). To extend the operating frequency of the MPF to W-band, we present a TOD precompensation technology implemented by a quadratic phase provider (QPP) device. Providing the OSP with an additional quadratic phase shift, the QPP can shift and extend the systematic TOD compensation range, thus resolving the operating frequency limit imposed by the conventional OSP-based technique. Combined with an automatic in-line TOD compensation procedure, the systematic TOD can be precisely compensated. With an almost complete cancelation of TOD in the filter, a tunable and reconfigurable single-passband W-band filter with a 3-dB bandwidth of around 15.5 MHz and a record-setting Q-factor of 6459 is obtained.

MISO current mode bi-quadratic filter employing high performance inverting second generation current conveyor circuit

This paper presents static and dynamic studies of a new CMOS realization for the inverting second generation current conveyor circuit (ICCII). The proposed design offers enhanced functionalities compared to ICCII circuits previously presented in the literature. It is characterized by a rail to rail dynamic range with high accuracy, a low parasitic resistor at terminal X (1.6Ω) and low power consumption (0.31mW) with wide current mode (3.32GHz) and voltage mode (3.9GHz) bandwidths.Furthermore, a new MISO current mode bi-quadratic filter based on using ICCII circuits asactive elements is proposed. This filter can realize all standard filter responses without changing the circuit topology. It is characterized by active and passive sensitivities less than unity and an adjustment independently between pole frequency and quality factor. The operating frequency limit of this filter is about 0.8GHz with 0.674mW power consumption.The proposed current conveyor circuits and bi-quadratic filter are tested by TSPICE using CMOS 0.18µm TSMC technology with ±0.8V supply voltage to verify the theoretical results.

Carbon nanotube antennas analysis and applications: review

Carbon nanotube characterized by additional inductive effect as compared with the traditional conductors like copper wires of the same size. Consequently, carbon nanotubes have high characteristic impedance and slow wave propagation in comparison with traditional conductors. Due to these characteristics, carbon nanotubes can be used as antenna. In view of this, we describe and review the present research progress on carbon nanotube antennas. We present different analysis models and results which are developed to investigate the characteristics of CNT antennas. Then we conclude by summarizing the characteristics of CNT antennas and specifying the operating frequency limit.

Design of Class E Amplifier With Nonlinear and Linear Shunt Capacitances for Any Duty Cycle

One of the main advantages of class E amplifiers for RF and microwave applications relies on the inclusion of a shunt capacitance in the tuned output network. At high frequencies, this capacitance is mainly provided by the output parasitic capacitance of the device with perhaps a linear external one for fine adjustments. The device's output capacitance is nonlinear and this influences the design parameters, frequency limit of operation, and performance of the class E amplifier. This paper presents a design method for the class E amplifier with shunt capacitance combining a nonlinear and linear one for any duty cycle, any capacitance's nonlinear dependence parameters, and any loaded quality factor of the tuned network. Nonlinear design with possibly different duty cycles is of relevance to maximize power or, alternatively, frequency utilization of a given device. Experimental, simulated, and compared results are presented to prove this design procedure

Growth of AlN piezoelectric film on diamond for high-frequency surface acoustic wave devices

Diamond films are very desirable for application to SAW devices because of their high acoustic wave velocity, which allows the extending of the frequency limit of operation at a given interdigital transducer line-width resolution. Use of high-quality AIN as the piezoelectric layer in conjunction with diamond is also desirable because of its high SAW velocity--the highest among all piezoelectric materials--together with its excellent electrical, mechanical, and chemical properties. The problems arising in the growth of A1N films on diamond have prevented, until now, the use of this combination of materials. In this paper we present recent results on the growth of highly oriented, low-stressed A1N films on diamond. SAW propagation on A1N/diamond has been theoretically investigated together with electromechanical coupling for both the Rayleigh and the Sezawa modes. The theoretical calculations show that high SAW velocities are achievable with good coupling efficiencies. Under proper conditions very large piezoelectric couplings are predicted--k2 = 2.2 and 4% for the Rayleigh and the Sezawa wave, respectively--comparable to those observed in strongly piezoelectric single crystals such as LiNbO3, but with SAW velocities approximately two-fold higher. Experiments performed on A1N/diamond/Si SAW test devices have shown good agreement between experimental results and theoretical predictions and demonstrate the feasibility of SAW devices based on this technology.

Evaluation of Frequency Behavior of Coils for Reference Magnetic Field Generation

The frequency behavior of coils for the generation of reference time-varying magnetic fields is evaluated starting from the coil construction parameters (geometrical dimensions, number of turns). A coil equivalent circuit with lumped parameters is considered and the related equation system is solved in the frequency domain. The computed frequency behavior of the coil impedance is validated by comparison with experimental data. The operating frequency limit is identified from the analysis of the coil impedance variation with frequency as a function of the construction parameters.

RTD Relaxation Oscillations, the Time Dependent Wigner Equation and Phase Noise

Wigner simulations of resonant tunneling diode (RTD) self-excited oscillations are discussed with respect to the upper frequency limit of operation and their sensitivity to large scale perturbations. These studies offer the most practical assessment of phase noise, response times of RTDs and of the coupling of quantum well space charge to its environment.

High frequency alternating current light-emitting diodes using Langmuir–Blodgett films

Alternating current (AC) light emitting diodes (LEDs) have been fabricated where Langmuir–Blodgett (LB) films of quinquethiophene (QT) or poly(3-hexylthiophene) (PHT) have been used as the active material sandwiched between insulating LB layers of poly(methylmethacrylate) (PMMA) or emeraldine base polyaniline (PANI), respectively. The frequency response of the devices has been studied, and as the frequency limit of operation we have used the −3 dB frequency. We have shown that high frequency AC LEDs can be fabricated with as few as 10–15 LB layers of the active material. Electroluminescence (EL) is observed almost equal in intensity in both biases for PMMA/QT/PMMA devices. The EL spectrum for these devices shows a broadening to the low-energy side as compared with the photoluminescence (PL) spectrum. The role of the interfaces for the frequency response is discussed.

On the Elimination of Reactive Element Loops and the Useof Special Approximations in the Design of OTA-C Filters

Loops of reactive elements in passive filters cause a series of problems in OTA-C simulations of these structures. These loops can be eliminated in a systematic way by the procedures described in the paper. The use of special approximations in the design of the passive prototype filters allows the elimination of multiple loops of reactive elements that appear in usual LC ladder filters with finite transmission zeros. This leads to more efficient active simulations, where problems with floating capacitors, DC or high-frequency instability, or limited operating frequency are avoided.

A Complete Analytical Theory of Self controlled Inverter Fed Synchronous Machine

A natural commutation inverter fed salient pole synchronous machine, with dampers in both axes is considered. Complete expressions are given for the currents during both the conduction and commutation intervals; they are based on the evaluation of the eigenvalues and eigenvectors of the equations which are derived from Park's model. All resistances are taken into account, for any value of frequency. It is shown how to determine the lower frequency at which natural thyristor turn-off can occur. An experimental method is proposed to find experimentally the lower frequency limit of operation.

New polar materials: Their application to saw and other devices

It has become increasingly clear in recent years that the two materials most commonly used in surface acoustic wave (SAW) devices (α-quartz and lithium niobate) have serious shortcomings for certain applications. For example, the relatively poor electromechanical coupling of α-quartz renders it unsuitable for devices requiring large bandwidths while the poor temperature coefficients of SAW velocities on LiNbO 3 renders this material unsuitable for many applications where environmental stability is important. Another important device limitation, which is determined by the properties of these materials, is the upper frequency limit of operation. This is currently fixed at about 1 GHz by the SAW velocities on LiNbO 3 and α-quartz of ~3400 and ~3200 m s -1 respectively. A large amount of work in recent years has gone into investigating the piezoelectric and elastic properties of new materials, with a view to finding one which either combines high electromechanical coupling with a zero temperature coefficient of SAW velocity or shows a significantly higher SAW velocity than α-quartz or LiNbO 3. The results of some of this work are reviewed and discussed in terms of the materials' crystal structures and the problems presented by their crystal growth. The prospects for new SAW and other piezoelectric devices fabricated using these materials are also discussed.

Development of a high-power transducer DUMILOAD

DUMILOAD (Dummy Mechanical Impedance LOAD) devices have been used to test transducers for many years. In concept the DUMILOAD consists of another specialized piezoelectric transducer mechanically coupled to the transducer to be tested. By varying the electrical impedance placed across the DUMILOAD’s electrical terminals, varying mechanical loads can be presented to the transducer being tested. Drawbacks to this approach have included the need for a cumbersome mechanical coupling device and the limited operating frequency band of the DUMILOAD. This paper describes some of the consideration involved in designing and constructing a DUMILOAD capable of operating at a power level of 1000 W in the frequency band from 3000 to 4000 Hz. Details of a ’’quick connect/disconnect’’ mechanical coupling device are also described. Subject Classification: [43]85.40;[43]30.85